Multimeter shows power when circuit breaker off

[ban-all-sheds]

I think you are getting confused between non-contact testers and multimeters. I agree that ideally a dedicated voltage indicator is better than a multimeter, but the behaviour the OP is describing is that of a non-contact tester, and that behaviour is not why multimeters should not be used.

 

[bhm1712]

Yes I agree I'm going off track

 

[Graham22]

Yes it's a multimeter with a non contact voltage tester setting.
I am curious what it is picking up. Even if the meters faulty, it's obviously is finding something and as mentioned earlier, I can only guess that's a phantom voltage induced from a parallel cable running alongside it, up to the loft.
My back is playing up so I have to leave it alone at present, but thought it interesting